344 



TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



Scorpcena dactyloptera either toward the high type of Trigla or toward the elongate low type 

 of Platycephalus. 



Heterosomata (Flatfishes, Soles) 



The outstanding feature of the skull of flatfishes is undoubtedly the transference of 

 both eyes to one side of the skull. Tate Regan (1929, p. 324) summarizes the embryo- 

 logical studies of Williams on this topic as follows: 



"Williams (Bull. Mus. Comp. Zool., 1902) has studied the migration of the eye; in the 

 cartilaginous skull of the larva two bars above the eye connect the lateral ethmoid cartilages 

 with the otic capsules; preparatory to the migration of one eye the bar above it is resorbed 

 and becomes reduced to projections of the lateral ethmoid and otic capsule with a gap 



pp&pareth 



-•/■^'pareth 



Hippo^lossu3 hippoglossus x_^42^' 



Fig. 224. Hippoglossus. Eyed side with twisted interorbital bar (fr'). 



between them. Through this gap the eye migrates until it reaches the other supraorbital 

 bar, when both eyes move to their final position, causing a torsion of the bar between them 

 which also affects the ethmoid region; when the shifting is complete ossification takes place, 

 and the main part of the frontal bone of the blind side forms on the wrong side of its eye. 

 Thus the essential feature of the skull of the flatfishes is that the interorbital bar is formed 

 mainly by the frontal of the eyed side and that the frontal of the blind side extends forward 

 to the ethmoid region outside the upper eye." 



In Figure 224 is shown the twisted interorbital bar of the frontal (/I) and the secondary 



